Taco Bell wants to liberate the "Taco Tuesday" trademark from a smaller, rival chain.

The taco chain filed a petition Tuesday (naturally) with the US Patent and Trademark office to cancel the trademark, owned by rival Taco John's for 34 years, because Taco Bell claims the commonly used phrase "should be freely available to all who make, sell, eat and celebrate tacos."

Since Taco John's owns the trademark, other restaurants and companies must seek permission to use "Taco Tuesday" in branding and advertising.

The use of the phrase "potentially subjects Taco Bell and anyone else who wants to share tacos with the world to the possibility of legal action or angry letters if they say 'Taco Tuesday' without express permission from [Taco John's] — simply for pursuing happiness on a Tuesday," the filing said.

Taco Bell added that "nobody should have exclusive rights in a common phrase."

Maggie Mettler, director of legal for Taco Bell's parent company, Yum! Brands, told CNN that it's using the trademark law to "remedy this injustice."

"It's a bold brand action that we hope others are willing to support," Mettler said.

Although Taco Bell's action sounds tongue-in-cheek, the company says it's serious. And it may have a strong case, because "Taco Tuesday" has become a commonly used phrase, according to trademark attorney Josh Gerben.

History of the phrase

"Taco Twosday" was coined by a Taco John's restaurant owner in the early 1980s to increase sales with a 99-cents deal for two tacos on its slowest day of the week. It worked, and sales turned around at the restaurant so much that the owner shared it with other franchisee owners.

The name was tweaked to "Taco Tuesday" and the chain trademarked the phrase in 1989, making it part of its marketing. Since then, Taco John's has defended its use of the phrase and sent cease-and-desist letters to others trying to use it.

"Over the years we've certainly asserted our trademark against national companies, restaurants big and small, and even pharmaceutical companies," former Taco John's marketing executive Billie Jo Waara said in a 2016 interview. "We also recognize that the unauthorized use [of Taco Tuesday] is prolific, and we do our best to communicate ownership."

"Taco Bell has not reached out to us, so we have no comment on any possible trademark action," Taco John's said in a statement. "Taco John's would like to thank our worthy competitors at Taco Bell for reminding everyone that 'Taco Tuesday' is best celebrated at Taco John's -- the trademark owner of Taco Tuesday."

In response, Taco John's is selling a "Taco Tuesday" deal of 2 tacos for $2 everyday until May 31.

What now?

Taco Bell is filing the petition with the Trademark Trial and Appeal Board, which is part of the US Patent and Trademark Office, and can take up two years before a decision is issued.

Taco John's has 40 days to file a response, and if the two chains can't reach an agreement, the case will move to a discovery period where each company can make document requests and present evidence stating their case. Following that would be a trial and oral arguments presented in front of the board's judges.

According to Gerben, Taco Bell has a "strong case" because US trademark law "prevents the registration of common phrases or phrases that become commonplace after a registration is granted."

In this instance, the slogan "has become a cultural phenomenon with a long history of being used by individuals and companies other than the current owner of the trademark," he told CNN.

Although Taco John's invented the phrase, that may not be a strong enough defense, Gerben said. The "Taco Tuesday" phrase is "widely used by Americans in a way that has nothing to do with the defendant's restaurant," he added.